The magnetoresistance effect generated by the spin polarized current flowing between the ferromagnetic electrodes through the nonmagnetic layer is great and thus is referred to as giant magnetoresistance effect (GMR) There are products such as magnetic heads and the sensors to which such an effect is applied. In addition, it is well known that the effect generated in a configuration in which a tunnel film is used instead of a nonmagnetic layer is referred to as tunneling magnetoresistance effect (TMR), and a characteristic better than GMR can be obtained. These elements are passive elements in which outputs are generated based on a relative spin angle between the ferromagnetic electrodes. When the antimagnetic layer is used as a semiconductor, there is an amplifying function in the semiconductor in addition to the magnetoresistance effect. Thus, active elements in spintronics have attracted attention. In Patent Documents 1 and 2, Spin-MOSFET is proposed in which magnetoresistance effect generated by spin polarized current flowing through a semiconductor is used.
In Non-Patent Document 1, there is a proposal that since spin is transported through the semiconductor, the tunnel film is inserted into the interface between the ferromagnetic body and the semiconductor considering to problem of conductivity mismatch. Actually, it is hard to introduce and transport the spin in the semiconductor layer if only the tunnel film is inserted. It relates to the increase of the element resistance of the entire circuit to insert the tunnel film so as to solve the problem of conductivity mismatch. Thus, it is hard to provide a giant magnetoresistance ratio.
There are two main reasons for the absence of a giant magnetoresistance ratio. One is a problem of spin attenuation associated with the spin dependent scattering in the vicinity of the interface between the ferromagnetic body and the semiconductor. The other is a problem concerning the design of the resistance.
The lower the carrier concentration is in the semiconductor channel layer, the easier the spin is accumulated and transported in the semiconductor channel layer. Spin transport distance is determined by the spin life referring to the average time during which spin continues until it attenuates and lose the spin polarization, and the diffusion coefficient with which the spin diffuses and transports. That is, the higher the electrical resistance of the spin-transport element is, the easier the spin is transported. On the other hand, the lower the resistance of the spin-transport element is, the easier the spin is introduced, and the speed can be higher and less energy will be used. Thus, in order to realize a spin-transport element in which high speed and energy saving is achieved while keeping good conductivity of spin, a contradiction concerning the electrical resistance property of the spin-transport element occurred.